Lighting systems typically include one or more light sources which is/are driven by a lighting driver. The lighting driver receives an input voltage and supplies power to the light source(s) in a format that is tailored to the requirements of the light source(s). In general, the lighting driver includes an electronic circuit and a housing for the electronic circuit.
A housing for an electronic circuit, and, in particular, a lighting driver circuit, may serve several purposes. One purpose of a typical electronics housing is to protect the electronic circuit (e.g. printed circuit board (PCB) assembly) from physical damage. Another purpose is to prevent an electrical shock which might occur if a human being comes into contact with the electronic circuit. Still another purpose is to insulate to PCB assembly from electrically shorting to nearby objects, such as a light source. Yet another purpose is to secure the PCB assembly and provide a means for it to be mounted or attached in a lighting fixture.
Lighting driver circuits, and particularly lighting driver circuits for light emitting diode (LED) light sources, can exhibit a relatively high leakage current. Also, it is often advantageous to have multiple LED lighting drivers within a single lighting unit. If a single LED lighting driver exhibits a relatively high leakage current, the use of multiple LED lighting drivers would be prohibited.
Therefore, the leakage current of the lighting driver circuit should be minimized to meet safety standards and to reduce or eliminate the danger of electrical shock. Accordingly, among other requirements, a main requirement for a housing for a lighting driver circuit is reducing or eliminating this leakage current. Also, for safety reasons, the housing needs to provide a protective isolation between the voltages of the lighting driver circuit and an external human being who may come into contact with the lighting driver.
To satisfy this requirement, some housings may be made of an electrically insulating material, such as a plastic. However, such housings have some drawbacks. For example, a plastic housing may not adequately shield the lighting driver circuit from external electromagnetic interference (EMI). Additionally, a plastic housing will not reduce the radiation emissions from the lighting driver circuit, which may exceed legally regulated emission limits. Furthermore, a large common mode current may be generated by the lighting driver circuit and the plastic housing cannot reduce this current. This will increase the overall radiated and conducted emissions of the lighting driver circuit unless a common mode filter with large capacitors is added.
To shield the lighting driver circuit from external EMI and to reduce the radiated emissions from the lighting driver circuit, some housings may be made of ferromagnetic material such as a metal, for example steel. The metallic housing may also serve as a heat sink, or may be directly connected to a heat sink, for the lighting driver circuit. The metallic housing may be directly connected to so-called “earth ground” for example via an input terminal connected to the lighting driver (e.g., via the “G” or green electrical wire in many electrical installations). Also, one or more safety capacitors may be provided between the metallic housing and the electrical ground of the lighting driver circuit to protect a human being from electrical shock. However such housings also have some drawbacks. For example, if larger safety capacitors are employed so as to lower their impedance and thereby reduce the common mode noise from the lighting driver circuit, then the leakage current from the lighting driver circuit will increase. On the other hand, if smaller safety capacitors are employed so as to lower their impedance and thereby reduce the leakage current from the lighting driver circuit, then the common mode noise from the lighting driver circuit will increase. Furthermore, these safety capacitors clamp the common mode surge capability of the lighting driver circuit, which is undesirable in many applications.
Thus, there is a need in the art to provide a housing for an electronic circuit, and in particular for a lighting driver circuit, which can address one or more of the drawbacks discussed above.